For sealing in the vicinity of an automotive engine, hitherto, there have been used oil-resistant gasket and packing members formed from cork, organic rubber, asbestos or the like. These members, however, are disadvantageous in that the inventory control and working process thereof are troublesome and that they are unreliable in sealing performance. In view of this, for such a use, an FIPG (Formed In Place Gaskets) system utilizing a cured product of a room temperature curing type silicone rubber composition has come to be adopted, whereby high evaluations have been obtained as to workability, hermetic seal properties, and heat resistance.
However, the known room temperature curing type organopolysiloxane compositions have the drawback that their cured products are insufficient in adhesion to oily surfaces. For instance, at the time of forming or punching an engine block, an oil pan or the like, deposition of a machine oil, a cutting oil, a turbine oil or the like occurs inevitably. In addition, after the room temperature curing type organopolysiloxane composition is applied to an engine block and before it is completely cured, an engine oil or the like may be poured into the engine block. Besides, in the case of a transmission (ATF (automatic transmission), CVT (continuously variable transmission)), the adherend surface may be fouled with an oil after assembly test. Therefore, due to the presence of the oily matter at the adhesive interface between the room temperature curing type organopolysiloxane composition and the engine block, the cured product functioning as a seal member may be defective in adhesion. Although this problem may be solved to a certain extent by thorough cleaning of the adhesive interface, the cleaning step takes considerable time and, hence, makes it difficult to carry out the engine assembling process in the same manner as before.
On the other hand, examples of a room temperature curing type organopolysiloxane composition somewhat improved in adhesion to oily surfaces are proposed in JP-A 5-98160 and JP-A 8-176445. In the former proposal, however, it is difficult to obtain good oily surface adhesive property, especially, good cohesive failure unless an oil-absorbing carbon powder is used as a filler in a large amount; besides, such a composition is so high in viscosity and thixotropy that the desired product is difficult to obtain. In addition, the high loading with the oil-absorbing carbon powder leads to easy absorption of the engine oil or the like into the cured product, so that a conspicuous lowering in hardness may be confirmed after the absorption of the engine oil. Moreover, the oil-absorbing carbon powder would absorb the silicone oil with time, causing the oily surface adhesion performance to be lowered with time. In the latter proposal, iminoxysilane is used as a crosslinking agent. The use of this curing agent results in that the curing type is limited to the deoxime type, which means poorness in general-purpose properties. In addition, even with such a curing agent used, it is difficult to obtain sufficient oily surface adhesive properties, particularly satisfactory cohesive failure, as comparable to that in the case of JP-A 5-98160.